For regulating the turbine or compressor output in an exhaust gas turbocharger, fluid-flow machines with a so-called variable turbine respectively compressor geometry are employed, which allow a variation of the inflow of a fluid such as for example exhaust gas or fresh air to the impeller of the fluid flow machine by means of adjustable guide blades. Such adjustability allows optimal adaptation of the fluid flow onto the impeller as a function of the fluid quantity entering at the moment. Adjusting the guide blades into an opening position with maximum flow cross section for the instance of a large quantity of exhaust gas or fresh air ensures that the gas molecules do not impinge on the impeller with too high a velocity. However, when the fluid quantity entering the fluid-flow machine decreases, for example because the internal combustion engine connected upstream of the turbocharger happens to be operated with low rotational speed at that time, adjusting the guide blades into a closing position with minimal flow cross section results in the gas molecules being accelerated. As a result, fewer gas molecules impinge on the impeller, however with increased velocity to that the impeller of the fluid-flow machine is accelerated.
For adjusting the guide blades between their opening and closing position, actuating devices, typically in the manner of actuating levers, are often used, which are directly or indirectly coupled—for example via a so-called adjusting ring—to the rotatable guide blades. For moving the actuating device designed as actuating lever it is opportune to connect the same to an actuator lever via a so-called actuating shaft in a rotationally fixed manner. By means of the actuator lever, which in turn can be drive-connected to an electric actuator, the actuating lever can thus be moved between the opening and the closing position. With conventional variable turbine and/or compressor geometries, the actuating shaft is usually at least partly in a bearing bushing provided on the guide blade support ring or on the housing and is rotatably mounted in the same. A variable turbine geometry constructed in this manner is known for example from EP 0 226 444 B1.